phosphor-power-sequencer/docs/power_loss.md

1 # Power Loss
5 Power distribution in a computer system is complex. It typically flows from a
6 wall outlet to power supplies to voltage regulators to system components. Other
7 devices may exist between the wall outlet and the power supplies, such as an
8 Uninterruptible Power Supply (UPS) or an Enclosure Power Distribution Unit
11 A **brownout** is a partial reduction in voltage to the power supplies. In some
12 situations, the standby voltage rails are still powered on but the main voltage
14 processor and other system components have lost power.
16 A **blackout** is a complete loss of power to the power supplies.
24 `phosphor-power-sequencer` application will take no action.
26 If the chassis was powered on when the brownout occurred, the power sequencer
27 device will normally change the chassis power good (pgood) signal from true to
28 false. `phosphor-power-sequencer` will isolate the failure to the power supply
29 rail. `phosphor-power-sequencer` will log a power supply error. This error will
30 specify the problem was the input voltage rather than the power supply hardware.
31 See [Power Good Faults](pgood_faults.md) for more information.
37 The system loses all power. It will be completely off until utility power is
40 When power is restored, if the system was previously powered on, it may be
41 automatically powered on again by the `phosphor-chassis-state-manager`
42 application. This depends on the Auto Power Restart settings.
46 If the blackout affects all chassis, the system loses all power. It will behave
51 - The `phosphor-chassis-power` application will do the following:
52   - Detect which chassis are experiencing a blackout.
53   - Set the `Status` property of the
54     `xyz.openbmc_project.State.Decorator.PowerSystemInputs` D-Bus interface to
56 - The `Available` property will be set to false for chassis that are
58   - This is due to the `PowerSystemInputs` `Status` property being set to
60 - If the BMC was reset by hardware due to the blackout, the following will
62   - `phosphor-power-sequencer` will read the pgood signal for each chassis and
64     `org.openbmc.control.Power` D-Bus interface for the chassis.
65     - For chassis experiencing a blackout, the `state` and `pgood` properties
67   - `phosphor-chassis-state-manager` will obtain the previous on/off state of
69   - `phosphor-chassis-state-manager` will determine if a power problem has
71     - At least one chassis was previously on and is now off.
72     - The host operating system is not running or communicating
73   - If a power problem has occurred, `phosphor-chassis-state-manager` will do
75     - Log an error
76     - Power the system [off](powering_off.md) and then [on](powering_on.md)
78       on.
80 See [Chassis Status](chassis_status.md) for more information on the D-Bus